The field of the invention is medical treatments generally and patient vascular access systems. The present invention relates to embodiments of a method and a system for detecting disconnection of an access needle or catheter while receiving medical treatment.
The maxim of “first, do no harm,” may be a good summary of the Hippocratic oath required of doctors and practiced by medical professionals. Nowhere is this principle required more than in modem medicine. With patients living longer, there are more extended treatments and more frail patients than ever. Such patients are in danger from a number of complications that can arise from continuing therapeutic procedures, and even from diagnostic procedures, that are necessary for their continued care. Treatments involving extra-corporeal blood treatment are clear examples.
The most obvious danger is infection, but the harm caused by infection can be overcome by not re-using even supposedly-sterile devices, by diligent attention by the patient himself or herself, and by the careful attention of care givers attending the patient. Other problems also arise, but, like infections, have been difficult to eradicate. One of the problems arises in blood treatment procedures in which the patient's blood is physically removed for treatment and then returned, all in the same procedure. Removal and return of blood is practiced in hemodialysis, for those persons whose kidneys do not function well. Other procedures, such as apheresis, involve removing blood from a patient or a donor to separate blood platelets or plasma from the red blood cells, and then returning the red blood cells to the patient or donor, as described in U.S. Pat. Nos. 5,427,695 and 6,071,421.
The extracorporeal medical treatments described above require that the blood be removed for treatment and then returned. This requires access to the patient's vascular system, from which blood is removed and to which blood is then returned. If a “batch” treatment is used, that is, a quantity of blood is withdrawn, treated and returned, only a single needle is used. Each batch treatment is typically short, and the treatment is attended by a medical professional at a clinic or hospital. Other treatments are continuous, such as the platelet separation discussed above, or dialysis treatment, and may require a duration of several hours or even overnight. Yet other treatments use a “batch” continuous method in which only a single needle is used. There are distinct withdraw and return phases in a batch continuous process. During the draw phase, blood is processed and additional blood is sent to a holding container to be processed during the return phase. In the return phase, blood is processed from the holding container and then returned to the patient or donor through the single needle.
Continuous treatments require two needles, or access points, one for withdrawal of blood and one for return. The withdrawal site is normally an artery, and a needle and a pump are used to provide the blood to the therapeutic machine, but in some treatments, such as apheresis, blood is withdrawn from and returned to veins. It is relatively simple to detect a problem with withdrawal, for instance, if the withdrawal needle is dislodged, using conventional air sensor technology. Detecting a problem in the return of the blood to the patient is more difficult. The return line typically includes a needle with venous access. If the return line is dislodged, the blood is not returned to the patient, but may continue to be pumped and may accumulate near the patient, but not returned to the patient's vascular system. Depending on the pumping rate of the blood and the time for treatment, this could have life-threatening effects on the patient within a very short period time.
Accordingly, a number of apparatuses have been devised for detecting needle dislodgement, especially venous dislodgement. Many of these techniques use pressure monitoring of the venous access line. One example is U.S. Pat. No. 6,077,443. This patent uses a pressure sensor mounted near a drip chamber to monitor pressure pulses from a blood pump. There appears to be very little difference between the signals when the access needle is properly in place and the signals when the access needle has been removed. In another example, U.S. Pat. No. 6,221,040, pressure-sensing equipment is made more sensitive, but this case results in a higher rate of false positives, i.e., false alarms.
Another method is disclosed in U.S. Pat. No. 6,572,576. This patent discloses periodically generating a negative pressure in the return line. This causes air to be drawn into the line, which can then be detected by a standard air sensor. This also has some negative aspects, since no air can be allowed in blood returned to the patient. Any mishandling in this area, such as that resulting from worn tubing, could result in blood in the air line with disastrous consequences. What is needed is an access disconnect device that overcomes these difficulties while providing a safe and quick indication to the patient or caregiver that a disconnect or a leak has occurred.